Golf clubs consist of an elongated shaft having an upper end upon which a hand grip is defined, and a club head is attached to the shaft lower end having a ball-striking face defined thereon. The ball-striking face is usually off center with respect to the longitudinal axis of the shaft, and upon striking a ball the radial distance between the point of ball impact with the head face with respect to the shaft axis will produce a torsional twisting force on the shaft as well as produce lateral shaft bending forces.
To improve the consistency and performance of golf clubs considerable effort has been expended toward the art of balancing the club and controlling the shaft bending characteristics. Typical examples of developments of this type are shown in U.S. Pat. Nos. 4,203,598 and 4,558,863. The configuration and technology of a golf club seam has also been the object of considerable research and typical disclosures of this type are shown in U.S. Pat. Nos. 1,942,445; 2,074,986 and 2,177,970.
To improve the performance of putters, concern has been expressed with respect to the alignment of the club head hosel axis and the club shaft, and U.S. Pat. No. 3,176,987 discloses apparatus for improving club assembly in this respect.
Prior to golf club shafts being made of metal and synthetic materials, club shafts were formed of wood sections cemented together, and in the wood club shaft art it was known to vary the physical characteristics of the shaft by using different types of wood at various circumferential locations of the shaft, and disclosures of this type are shown in U.S. Pat. Nos. 1,626,476 and 1,626,477.
To date, by far the greatest percentage of golf club shafts are formed of metal, while materials such as fiberglass, graphite and the like are also employed. Such shafts have a much greater strength than wood shafts, and are able to produce a stronger and more consistently functional operation than wood shafts. In the manufacture of such non-wood shafts a single longitudinally extending seam is employed to maintain the cylindrical configuration of the shaft and the art of forming golf club shafts is highly developed as illustrated in U.S. Pat. Nos. 1,942,445; 2,074,986 and 2,177,970. The art of manufacturing golf club shafts has progressed to the point that the shaft seam is invisible both exteriorly and interiorly of the hollow shaft, and the presence of the seam does not visually distract from the shaft appearance.
Most golf club seams, particularly with metal shafts, are of a butt weld wherein the shaft is formed by rolling the shaft blank into a tapered substantially cylindrical configuration so that the ends of the blank are in opposed relationship and are butt-welded together to maintain the shaft configuration. While this welding operation may be so accurately accomplished as to prevent the seam from being visible, the presence of the seam does affect the torsional and bending characteristics of the shaft. For instance, the location of the seam adds a "stiffness" to the lateral bending shaft characteristics, and also affects the shaft torsional characteristics with respect to the shaft axis. Thus, the shaft seam affects the physical characteristics of the shaft and deflection and recovery of the shaft upon a golf ball being struck. Such shaft characteristics will, to a considerable extent, affect the flight trajectory of the ball.
Presently, to the inventor's knowledge, no golf club manufacturer is assembling golf club shafts and heads wherein the shaft seam is oriented in a predetermined manner to the club head or head ball-striking face. Most golf club shafts and club heads are assembled by inserting the lower end of the shaft within a cylindrical recess defined in the head hosel and epoxy is used to maintain the shaft within the club head hosel recess. The shaft and head are assembled without regard to the rotational position of the shaft with respect to the head, and without regard to the location of the shaft seam adjacent the head with respect to the head ball-striking face. Thus, present golf club manufacturers are oblivious to the relationship of the seam to the golf club face, and even if it was desired to relate the shaft seam to the head face, such an orientation is very difficult to achieve as the position of the shaft seam with respect to the shaft cannot readily be determined.
Accordingly, because of the haphazard assembly of the shaft and head with respect to the location of the shaft seam, many golf clubs have a "built-in" reaction to the forces imposed upon the club during impact with a ball which may tend to "hook" or "slice" the ball. Only if the seam happens to be located at a "neutral" location can such inherent characteristics be eliminated from the club. Also, it is most likely that, even in a set of "matched" clubs, the seam of each club shaft will be oriented to the associated club head face in a different angular relationship imparting to each club of a set different characteristics with respect to bending and torsion which works against the golfer's desire to produce uniform results with different clubs. Avid or professional golfers often find "favorite" clubs which feel right to them and often use mismatched clubs with which consistent results are achieved. Although it has not been previously appreciated, such consistency between various different clubs in a mismatched set is very likely to be due to the fact that the club shaft seams are oriented to the club head in a manner which substantially eliminates adverse influences of the shaft seam on the club operation.
It is an object of the invention to provide a method of assembling a seamed golf club shaft and head wherein predetermined torsional and bending characteristics of the club during use can be achieved.
Another object of the invention is to provide a golf club having a seamed shaft wherein the seam is so related to the club head that the adverse effect of the shaft seam to the characteristics of club shaft bending and torsion forces are eliminated or neutralized.
Yet another object of the invention is to provide a golf club having a seamed shaft wherein the shaft seam is so oriented to the club head face that the seam is in a "neutral" location with respect to the head ball-striking face as to eliminate reaction forces within the club shaft which adversely affect the flight of a struck ball.
Yet another object of the invention is to provide a golf club having a seamed shaft wherein the location of the shaft seam to the club-striking face is oriented in a predetermined manner to compensate for deviations within the particular user's golf swing.
Yet an additional object of the invention is to provide a set of a plurality of golf clubs having seamed shafts attached to heads wherein the relationship of the seams of each club shaft are pre-oriented to render the clubs of the set with consistent physical bending and torsional characteristics to provide a consistency of club operation for the entire set.
To practice the invention it is first necessary to locate the position of the seam of a seamed golf shaft. Golf club shafts are usually of a tapered configuration, the larger diameter end having a hand grip mounted thereon, and the smaller diameter end being attached to the club head. The shaft seam which occurs during the manufacture of most club shafts extends longitudinally the length of the shaft, and throughout its length is substantially consistently related to the circumferential configuration of the shaft, i.e. the rotational location of the seam relative to the shaft axis remains substantially constant with respect to the shaft length.
Locating the shaft seam on the circumference of the hollow shaft is often difficult due to the expertise used in forming the seam, which is usually of a butt-weld type. An acceptable manner for locating the seam is to place the shaft under a bending stress while the shaft is rotated about its axis and the flexing characteristics of the shaft during such bending and rotation can be readily discerned as the bending characteristics fluctuate in accordance with the location of the seam. In this manner the location of the seam on the shaft may be accurately determined.
After the shaft seam is located, its location is marked, and when assembling the club head to the lower end of the shaft, the seam is oriented to the head ball-engaging face in a predetermined manner. Usually, the head hosel includes a socket having a diameter slightly greater than that of the shaft lower end as to closely receive the shaft lower end and assembling of the shaft and head is produced by using an epoxy adhesive to affix the shaft within the hosel socket.
When locating the shaft seam to the club ball-striking face it is usually desired that the seam be located at a "neutral" location with respect to the club face and the forces imposed upon the club upon the head engaging a ball. By reference to a "neutral" location it is meant that the seam is so oriented to the club face that the influence of the club seam upon the bending end torsional characteristics of the shaft do not adversely affect the flight of the struck ball. Experience has shown that the preferred location of the shaft seam is at the "rear" of the club with respect to the direction of club movement during the normal club swing when striking a ball. Thus, in most instances, the shaft seam will be located 180.degree. opposite to the direction of movement of the club head during the club swing. However, it is also possible to locate the seam at the "front" of the club, i.e. in the direction of swing movement, and it is conceivable that location of the seam at either of the 90.degree. locations with respect to the rear or front of the club would produce a "neutral" reaction which would not significantly adversely affect the ball movement.
By locating all of the seams of the shafts of a set of golf clubs, either woods or irons, or both, the bending and torsional characteristics of each club will be the same and a user will be assured of uniform club response and reaction regardless of which club is being used.
Because of the "stiffness" of the club shaft adjacent the welded seam it is possible to use the adverse effect of obliquely relating the position of the club seam with respect to the club face to overcome deviations in the golf swing of a particular golfer. Many golfers have an incorrect golf swing which will cause the ball to hook to the left or slice to the right due to an improper movement of the club head with respect to the ball. By locating the shaft seam to the club head it is possible to produce a golf club which has a slight inherent hook or slice built into the club, and by orienting the seam to the club head in such a manner to compensate for the deviations of the golf swing of a particular golfer, the club can be "customized" for a particular golfer to minimize the effect of an improper swing. Likewise, if a golfer's swing should slightly vary with respect to the use of woods or irons, or even particular clubs within the wood or iron set, each club can be "customized" for a particular golfer with respect to the location of the shaft seam to the club head.